Fuel Tank Replacement near St. Louis, Missouri

When the EVAP system is checked, the purge valve and vent valve are closed, and the pressure is monitored by the fuel tank pressure sensor. If that pressure drops with both valves closed, there is a leak in the EVAP system. If pressure holds properly, the system passes, and will continue to prevent vapor emissions. The sensor is also used in testing vent valve and purge valve operation. When the valves are open, the pressure sensor reads the fuel tank pressure, and must sense a drop in pressure. If not, the purge valve or vent valve may be faulty.